Symptoms and causes

Symptoms

Signs and symptoms of hypertrophic cardiomyopathy may include one or more of the following:

Shortness of breath, especially during exercise

Chest pain, especially during exercise

Fainting, especially during or just after exercise or exertion

Sensation of rapid, fluttering or pounding heartbeats (palpitations)

Heart murmur, which a doctor might detect while listening to your heart

When to see a doctor

A number of conditions can cause shortness of breath and heart palpitations. It's important to get a prompt, accurate diagnosis and appropriate care. See your doctor if you experience any symptoms associated with hypertrophic cardiomyopathy.

Call 911 or your local emergency number if you experience any of the following symptoms for more than a few minutes:

Rapid or irregular heartbeat

Difficulty breathing

Chest pain

Causes

Hypertrophic cardiomyopathy is usually caused by abnormal genes (gene mutations) that cause the heart muscle to grow abnormally thick. People with hypertrophic cardiomyopathy also have an abnormal arrangement of heart muscle cells, a condition known as myofiber disarray. This disarray can contribute to arrhythmia in some people.

The severity of hypertrophic cardiomyopathy varies widely. Most people with hypertrophic cardiomyopathy have a form of the disease in which the wall (septum) between the two bottom chambers of the heart (ventricles) becomes enlarged and impedes blood flow out of the heart. This condition is sometimes called obstructive hypertrophic cardiomyopathy.

Sometimes hypertrophic cardiomyopathy occurs without significant blocking of blood flow. However, the heart's main pumping chamber (left ventricle) may become stiff, reducing the amount of blood the ventricle can hold and the amount pumped out to the body with each heartbeat. This condition is sometimes called nonobstructive hypertrophic cardiomyopathy.

Risk factors

Hypertrophic cardiomyopathy is usually inherited. There's a 50 percent chance that the children of a parent with hypertrophic cardiomyopathy will inherit the genetic mutation for the disease. Close relatives — parents, children or siblings — of a person with hypertrophic cardiomyopathy should ask their doctors about screening for the disease.

Complications

Many people with hypertrophic cardiomyopathy (HCM) don't experience significant health problems. But some people experience complications, including:

Arrhythmias. Thickened heart muscle, as well as the abnormal structure of heart cells, can disrupt the normal functioning of the heart's electrical system, resulting in fast or irregular heartbeats. Atrial fibrillation, ventricular tachycardia and ventricular fibrillation are among the arrhythmias that may be caused by hypertrophic cardiomyopathy. Atrial fibrillation can also increase your risk of developing blood clots, which can travel to your brain and cause a stroke.

Dilated cardiomyopathy. Over time, thickened heart muscle may become weak and ineffective in a very small percentage of people with HCM. The ventricle becomes enlarged (dilated), and its pumping ability becomes less forceful.

Mitral valve problems. The thickened heart muscle can leave a smaller space for blood to flow, causing blood to rush through your heart valves more quickly and forcefully. This increased force can prevent the valve between your heart's left atrium and left ventricle (mitral valve) from closing properly. As a result, blood can leak backward into the left atrium (mitral valve regurgitation), possibly leading to worsening symptoms.

Heart failure. The thickened heart muscle can eventually become too stiff to effectively fill with blood. As a result, your heart can't pump enough blood to meet your body's needs.

Sudden cardiac death. Ventricular tachycardia and ventricular fibrillation can cause sudden cardiac death. People with hypertrophic cardiomyopathy have an increased risk of sudden cardiac death, although such deaths are rare. Sudden cardiac death is estimated to occur in about 1 percent of HCM patients each year. Hypertrophic cardiomyopathy can cause heart-related sudden death in people of all ages, but the condition most often causes sudden cardiac death in people under the age of 30.

AskMayoExpert. What tests are needed to confirm the diagnosis of hypertrophic cardiomyopathy (HCM) and what is the role of genetic testing? Rochester, Minn.: Mayo Foundation for Medical Education and Research; 2014.

A single copy of these materials may be reprinted for noncommercial personal use only. "Mayo," "Mayo Clinic," "MayoClinic.org," "Mayo Clinic Healthy Living," and the triple-shield Mayo Clinic logo are trademarks of Mayo Foundation for Medical Education and Research.